1. Field of the Invention
The present invention relates to an image-blur correcting optical system suitable for a viewing optical apparatus with an image-blur correcting function.
2. Description of the Related Art
As an image-blur correcting optical system for a viewing optical apparatus, such as a binocular, a telescope and the like, the optical system, for example, disclosed in Japanese Unexamined Patent Publication No. Hei-10-186228 is known in the art. The image-blur correcting optical system disclosed therein is provided in an objective optical system constituted by a front lens group and a rear lens group, in this order from the object. An image-blur correction is conducted by moving the negative rear lens group in a direction substantially perpendicular to the optical axis. This image-blur correcting optical system is designed to be used in a viewing optical apparatus, such as a spotting scope, having a very long objective optical system. Therefore in order to provide an image-blur correcting apparatus (e.g., an actuator) in the objective optical system, a sufficient space for that purpose is secured therein. Further, since a negative lens element is used as an image-blur correcting lens element to shorten the objective optical system, the overall length thereof is less than or equal to the focal length of the objective optical system, which contributes to miniaturization of a viewing optical apparatus. Due to the above arrangement of the objective optical system, the spotting scope can be made enough short; however, the same arrangement is still considered to be too long for an objective optical system for a binocular or the like. Accordingly, the above image-blur correcting optical system cannot be applied to a viewing optical apparatus, such as a binocular or the like, in which the overall length of the objective optical system is inherently short and no sufficient space is maintained for an image-blur correcting apparatus.